This invention relates to dispensing devices that employ a heat source to promote the release of a volatile material from a wick. More particularly, the invention relates to improved wick assemblies for use with such devices.
A variety of devices for dispensing volatizable materials into the atmosphere are known. Such volatizable materials may be air scents (e.g. fragrances), pest control materials (e.g., insecticides), allergen control ingredients, disinfectants, or other chemicals.
In one such type of device a lower reservoir is provided into which a wick extends. The wick draws the active chemical up from the reservoir to an area where there is a heat source. The heat source then promotes dispensing of the volatile to the environment. Such devices are plugged into an electrical wall outlet to supply power to an electrical heating coil. Optionally, such devices may also have a fan or other means to further promote evaporation or dispensing.
Prior art examples of such devices include U.S. Pat. Nos. 6,361,752, 5,647,053, 5,290,546, 5,222,186, 5,095,647, 5,038,394, and 4,663,315. The disclosure of these patents and all other publications referred to herein, are incorporated herein by reference as if fully set forth.
While the foregoing prior art devices have a number of advantages, they also have some deficiencies, particularly with respect to the wicks used with them. For example, when some of these devices are used to dispense certain volatile materials, certain wicks can clog. Other wicks are less susceptible to clogging, but are too brittle to use in certain automated assembly operations. Still other wicks tend to draw liquid too fast, creating a “drool” problem or inefficient use of certain actives. Some other wicks are not sufficiently thermally resistant to use with some types of heating devices.
One improvement is described in a U.S. patent application (of our assignee) filed on Jan. 30, 2003 with U.S. Ser. No. 10/354,876. That application disclosed providing an array of granular particles such as sand coated with a polymer binder to form a network of pores in the wick which were less susceptible to clogging. However, this type of wick was not physically strong enough to resist the mechanical stresses encountered in some automated assembly operations. This added some cost to the assembly of such wicks with devices that use them.
In unrelated work there have been some disclosures of certain types of multi-part wicks. See e.g. U.S. Pat. Nos. 4,416,616 and 3,262,290 and European Patent Application No. EP 0 897 755 A2. However, these wick constructions have not been suggested as a solution to the above problems, and in any event the means of associating the wick parts are not desirable for the present applications.
Thus, there is a need for improved wick assemblies that address the above deficiencies of the prior art.